Folding cartons used to package a variety of different products are formed in packaging machines from folded carton blanks. The folded blanks are basically in the form of collapsed sleeves formed by the carton blank manufacturer from a flat blank comprised of foldably connected panels. To form a collapsed sleeve, a glue flap connected to one of the end panels is adhered to the edge portion of the opposite end panel after the blank has been folded into proper position. In such a blank the tabs or flaps which eventually form the ends of the package are in unfolded condition extending from the leading and trailing ends of the blank as it moves through the blank forming machine.
While it is of course essential to apply a sufficient amount of glue to the glue flap to hold the carton together, it is also important not to apply so much that it squeezes out from between the glue flap and the opposite end panel during formation of the collapsed folded carton blank. When this occurs, the collapsed carton blanks may adhere to each other in the stacks in which they are shipped, and the excess glue may prevent the collapsed blanks from being opened in the final packaging operation. If collapsed blanks cannot be readily opened in the packaging machine, the blanks jam up, requiring the machine to be shut down to remove the jam. This slows the overall packaging process considerably and is to be avoided if at all possible.
Glue is conventionally applied by a glue wheel to carton blanks having only one glue line. Although glue wheel application is desirable from the standpoint of assuring that sufficient amounts of glue are applied during a high speed collapsed carton blank forming operation, the difficulty in controlling the quantity applied gives rise to the problem of excessive glue application. In addition, variations in operating conditions, such as in the paperboard thickness and in the pressure applied by the press rolls used to press the glue flap and opposite end panel together, can also cause glue to be squeezed out from between the glued segments.
It would be highly advantageous to be able to better control the gluing operation to prevent the application of excessive amounts of glue. It would also be desirable to control the gluing operation in a manner which does not require extensive changes to the blank forming machine and does not require it to run slower.